Comparison of the in sacco rumen and washing loss methods to estimate the potential energetic value for livestock of leaves from tropical trees, shrubs and crop residues

Abstract

Samples of leaves from ten tropical species: six trees (Acacia mangium, Acacia auriculiformis, Gliricidia sepium, Leucaena leucocephala, Indigofera teysamii, Jackfruit - Artocarpus heterophyllus), three crop plants (Cassava - Manihot esculenta, sugar cane - Saccharum officinarum, banana - Musacea) and a crop residue (Rice straw - Oryza sativa) were put in nylon bags and the losses of dry matter were estimated for washing times of 30, 60, 90 and 120 minutes in a commercial semi-automatic washing machine, and incubation times of 6, 12, 24 and 48 hours in the rumen of a cow fed rice straw and fresh grass (Panicum maximum). The relationships between losses of dry matter in the washing machine and time of washing were curvilinear (range of R2 from 0.86 to 0.99) for all leaves except those from banana and Acacia auriculiformis where the relationship was linear (R2=0.99). There were close relationships between in sacco dry matter loss after 48 hours incubation and dry matter losses by washing (R2=0.73, 0.80, 0.86 and 0.80 for washing times of 30, 60, 90 and 120 minutes [average values for all samples at each time were used in this analysis]). Selecting the 90 minute washing time and correlating the data obtained with this method (range 15-47% for the ten species) with those from the 48 hour in sacco dry matter loss (range 25-61%) gave an R2 of 0.86. The two methods ranked the species similarly and were considered to be equally effective in rating the chosen materials as potential sources of digestible dry matter for both ruminant and monogastric livestock. The use of the washing loss method is recommended as a first approximation to estimation of nutritive value as it is simple, rapid, and low cost, and dispenses with the need for surgically modified animals.